The combination of her reportage and the release of her content brought her fame and led to a grand jury investigation and financial increase in the Department of Public Charities and Corrections.

Penniless after four months, she talked her way into the offices of Joseph Pulitzer's newspaper the New York World, and took an undercover assignment for which she agreed to feign insanity to investigate reports of brutality and neglect at the Women's Lunatic Asylum on Blackwell's Island.

The hospital staff seemed unaware that she was no longer "insane" and instead began to report her ordinary actions as symptoms of her illness.

The food consisted of gruel broth, spoiled beef, bread that was little more than dried dough, and dirty undrinkable water.

I would like the expert physicians who are condemning me for my action, which has proven their ability, to take a perfectly sane and healthy woman, shut her up and make her sit from 6 a.m. until 8 p.m. on straight-back benches, do not allow her to talk or move during these hours, give her no reading and let her know nothing of the world or its doings, give her bad food and harsh treatment, and see how long it will take to make her insane.

Even when the water was eventually changed, the staff did not scrub or clean out the bath, instead throwing the next patient into a stained, dirty tub.

[8] Nellie recalled the bathing ritual with trepidation, stating: My teeth chattered and my limbs were goose-fleshed and blue with cold.

Of her release, Bly wrote: I left the insane ward with pleasure and regret–pleasure that I was once more able to enjoy the free breath of heaven; regret that I could not have brought with me some of the unfortunate women who lived and suffered with me, and who, I am convinced, are just as sane as I was and am now myself.The question in hand was how Nellie managed to convince professionals of her insanity in the first place.

A low-budget independent film version of 10 Days in a Madhouse, starring Caroline Barry as Bly, Christopher Lambert, Kelly Le Brock and Julia Chantrey, was released in 2015 from Pendragon Pictures.

Investigative journalist Lana Winters enters Briarcliff Asylum on false pretenses with the intent of exposing patient abuses, only to be discovered and committed for being a lesbian.

In September 2017, a TV series was announced based on 10 Days in a Mad-House, written by Sarah Thorp, starring Kate Mara as Bly, executive produced by Mara, Thorp, and Carolyn Newman for Entertainment One, Danjaq and The Frederick Zollo Company.

[14] On September 21, 2023, an original opera by composer Rene Orth and librettist Hannah Moscovitch entitled "10 Days in a Madhouse" premiered at the Wilma Theater as part of the O23 Festival.